This invention relates to radiant energy transmission, and more particularly to a more efficient coupler for the junctions of fiber optics cables.
The employment of fiber optic cables for various types of communication systems has become a rapidly expanding art. And, as would be expected much development has been devoted to the production of low-loss glass materials and cables, and the design of couplers for joining such cables. Coupling members have been proposed to optimize coupling efficiency which is a necessary objective if optical communication is to be feasible when applied to long cable systems and/or multi-port applications.
To increase coupling efficiency, the principal thrust of the prior art has been directed to reducing Fresnel losses by minimizing the separation distance between axially aligned cable junctions by creating so-called "butt junctions." However, such designs possess fundamental coupling deficiencies in the inability to align a multiplicity of randomly oriented small diameter fibers on a one-to-one basis between the transmitting cable junction and the receiving cable junction, considering the high packing fraction losses resulting at the latter junction.
The present invention is directed to the unique concept of treating the entire bundle of fibers at the cable junctions as point sources of propagating and receiving energy rather than a multiplicity of energy sources. This objective is achieved by the use of a specially designed optical lens which also reduces extraneous internal and external energy reflections through and between the lenses to enhance the efficiency of the coupler.
In the past, some fiber optic couplers have utilized optical lens for combining optical rays. For example, U.S. Pat. No. 3,508,807 teaches the combining of different colored light from three light bundles into white light in a single bundle through the use of a pair of plano-convex lens which of necessity are spaced from each other and from the respective ends of the fiber optic cable junctions to provide a mixing of the colors. There is no recognition in this patent of the high transmission losses caused by the various air/lens interfaces which exist in patentee's construction because the primary interest is to mix various colors.
A similar light coupler is shown in U.S. Pat. No. 3,912,364 for combining two light transmitting cables into a single light cable through a double convex lens mounted in an enclosure and spaced from the cable junctions, the latter located at the focal points of the lens. This device projects a multiplicity of light beams, and the large lens/air interfaces causes high light losses in the light combiner.